Medianet Reference Guide - Cisco

Network Availability Technologies
Chapter 3
Medianet Availability Design Considerations
You can enable PortFast globally (along with BPDU Guard), or on a per-interface basis, by entering the
following commands:
Switch(config)# spanning-tree portfast default
Switch(config)# spanning-tree portfast bpduguard default
UplinkFast provides fast convergence after a direct link failure and achieves load balancing between
redundant Layer 2 links, as shown in Figure 3-11. If a switch detects a link failure on the currently active
link (a direct link failure), UplinkFast unblocks the blocked port on the redundant link port and
immediately transitions it to the forwarding state without going through the listening and learning states.
This switchover takes approximately one to five seconds.
Figure 3-11
UplinkFast Recovery Example After Direct Link Failure
Switch A
(Root)
L1
Switch B
L2
Link failure
Switch C
L3
UplinkFast transitions port
directly to forwarding state
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UplinkFast is enabled globally, as follows:
Switch(config)# spanning-tree uplinkfast
In contrast, BackboneFast provides fast convergence after an indirect link failure, as shown in
Figure 3-12. This switchover takes approximately 30 seconds (yet improves on the default STP
convergence time by 20 seconds).
Figure 3-12
BackboneFast Recovery Example After Indirect Link Failure
Switch A
(Root)
L1
Link failure
Switch B
L2
L3
Switch C
BackboneFast transitions port
through listening and learning
states to forwarding state
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BackboneFast is enabled globally, as follows:
Switch(config)# spanning-tree backbonefast
These Cisco-proprietary enhancements to 802.1D STP were adapted and adopted into a new standard for
STP, IEEE 802.1w or Rapid Spanning-Tree Protocol (RSTP), which is discussed next.
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Medianet Reference Guide
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